Since passive matrix type liquid-crystal display devices need no costly switching elements and are less expensive than active matrix type liquid-crystal display devices, the passive matrix type liquid-crystal display devices find widespread use as monitors of portable computers and portable electronic apparatuses.
The following methods are known as the methods of driving the passive matrix type liquid-crystal display device.
(1) APT method (IEEE TRANSACTIONS OF ELECTRON DEVICE, VOL, ED-21, No. 2, FEBRUARY 1974 P146-155 "SCANNING LIMITATIONS OF LIQUID-CRYSTAL DISPLAYS" P. ALT, P. PLESHKO, ALT&PLESHKO TECHNIC).
(2) Smart Addressing (LCD International '95, Liquid-Crystal Display Seminars held under the sponsorship of Nikkei BP, C-4 Lecture No. (1), by Matsushita of Tottori SANYO Electric, Co., Ltd).
(3) Multi-line driving methods (for example, Japanese Patent Application 4-84007, Japanese Unexamined Patent Publication No. 5-46127, and Japanese Unexamined Patent Publication No. 6-130910).
Besides the demand for miniaturization and light weight, there is a growing demand for longer time of displaying without the need for battery replacement in the field of the portable electronic apparatuses such as cellular telephones and pagers. Therefore, a low power consumption feature is rigorously required of the display device used in such portable electronic apparatuses.
The inventor of this invention has extensively studied the passive matrix type liquid-crystal display device with a view to reducing power consumption.
The study has shown that prior art passive matrix liquid-crystal display devices have to supply an alternating current of 20 V or higher in amplitude to both scanning lines and signal lines even during a display-off time, that the power consumption in the power supply circuit for generating that alternating current is considerably large, and that currents flowing between the scanning lines and the data lines via liquid crystals are also considerably large.
The present invention has been developed with a view to resolving such problems.